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Weekly vegetable update 8/16/23: Iowa State Fair special!

Authors: Natalie Hoidal and Marissa Schuh

Our team is in Iowa this week for the National Association of County Agricultural Agents annual meeting, so we’re bringing you a special issue of vegetables from the Iowa State Fair. While the attractions the fair is known for are butter statues and beef sundaes (don’t ask), the state fair vegetable displays were the prime attraction for us.

Whatever was in the rulebooks for the state fair vegetable judging had us (and incidentally, every other vegetable extension person at the conference) scratching our heads. But even in a room of blue ribbon “longest beans” and “best display of purple and orange vegetables,” physiological and pest issues abounded. We applaud the gardeners of Iowa for their hard work in growing the vegetables filling the Iowa State Fair Horticulture building, and we encourage the organizers to consider giving awards for vegetables presenting common vegetable issues.

Veg on veg on veg. Every person in the picture is an extension educator from somewhere in the US. Photo: Marissa Schuh, UMN Extension

Tomato spots: stinkbugs, thrips, or disease?

In dozens of entries of all types of tomatoes, spotting was a common sight.. These spots can be the results of insect feeding or disease.

The last month has seen the hatching of brown marmorated stink bug (in addition to all the species of stink bug that have been in Minnesota for a while). Stinkbug feeding appears as pale (in green tomatoes) to yellow (in red tomatoes) spots on the surface of the fruit. If you cut the tomato and bisect the spots, if stink bugs did the feeding, the area around the spot will be white. The discoloration and unripened areas surrounding the feeding are the results of stinkbugs feeding with their straw like mouthpart.

A discrete spot of stinkbug feeding. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,

Thrips are small, yellow oblong insects with a mouthpart that is a little similar to stink bugs. Instead of being a straightforward straw, thrips mouthparts have that piece but also scrape (rasp is the entomological term). This feeding causes golden flecks. These are often in a circular pattern that mirrors where tomato fruits were touching each other on the plant (thrips hang out in protected areas).

Thrips feeding on tomato. Photo:Cornell University Long Island Horticultural Research & Extension Center

Viruses can also cause spotty discoloration, though it often appears across all fruit on a plant (as well as sometimes leaf symptoms). These spots can vary in color and appearance depending on the virus, but viruses tend to cause fruit distortion.

Tomato fruit showing tomato spotted wilt virus symptoms. William M. Brown Jr.,

Tomato growing pains: cracks and splitting

We’ve talked about splitting in tomatoes and tomatillos in recent updates, but we saw a few other conditions at the fair this week that are physiological consequences of weather fluctuation.

The first is catfacing, which happens when the blossom end scar becomes enlarged, causing growth deformities. Catfacing is not well understood, but researchers think that it can happen when there are cold temperatures during flowering, or significant fluctuations in daily high and low temperatures.This can also happen when thrips feed on the blossom end of the fruit. High soil nitrogen concentrations may exacerbate it.

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, 

Tiny growth cracks around the stem end of tomato fruit can happen with fluctuating water levels. Specifically this is most common when there is a flush of moisture following a dry period. Larger cracks create openings for secondary pathogens or even insects to enter the fruit, while smaller, more subtle cracking may not impact marketability depending on your markets.

Photo: Natalie Hoidal

Yellow shoulder

We’ve written about yellow shoulder in previous articles, but wanted to mention it again after seeing quite a few tomatoes with yellow shoulder this week, and because it may be co-occuring with other problems.  

Paul Bachi, University of Kentucky Research and Education Center,

Yellow shoulder is one of those issues that can stem from multiple causes including very hot weather, potassium deficiency, or direct sun exposure. However, we also see it when tomato plants have pathogens that cause the stems to become cankerous since dead stem tissue isn’t able to efficiently transport nutrients. In particular, we’ve noticed yellow shoulder co-occuring with Clavibacter / bacterial canker, which has been spreading across Minnesota in recent years. If you look up this pathogen you’ll see dramatic lesions on fruit, but in our anecdotal experience, it typically has to get really bad before you start to see fruit lesions. We typically first notice yellow shoulder and leaf symptoms when this pathogen first shows up on a farm. If you’re seeing a lot of yellow shoulder, take a step back and investigate your plants for signs of disease on the leaves, stems, and roots. 

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo,


The sporadic, huge flushes of rain some areas have received have led the the development of Edema (or oedema) on a couple of crops we saw. If you see cabbage, squash, or pumpkins with scabby, almost peanut like texture, what you are seeing could be edema. This condition is almost like splitting in tomatoes, where there in an influx of water and cells burst. In crops afflicted by edema, these bursts are as the cellar level, and scab over, giving affected areas a tan, rough appearance.

Edema in cabbage. David B. Langston, University of Georgia,


Potato scab

We saw quite a bit of potato scab on the state fair potatoes. Scab can look different depending on the species of potato, the soil, and environmental conditions; it can show up as raised lesions, surface spots, or sunken lesions. It’s most common during warm weather and in dry soil during the 2-6 weeks following tuber initiation, so it’s not surprising that we’re seeing a lot of it this year.

Scab is another pathogen that thrives in environments with a lot of decomposing organic matter, and so as farmers utilize deep compost mulch systems or add a lot of compost to fields, this may make the soil more hospitable to scab.

While it’s ok to eat peeled potatoes that have scab, this disease impacts marketability and storage (scab lesions may be more susceptible to common storage pathogens like soft rot). Read more about potato scab here.


Clemson University - USDA Cooperative Extension Slide Series ,

Sandra Jensen, Cornell University, 

Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, 

Rodent damage

We also saw, especially in the giant vegetables section, rodent damage. Rodent damage in pumpkins not destined for human consumption may scab over and have shorter shelf life. Other vegetables with visible rodent damage should not be sold. Look out for chunks missing out of fruit that aligns with where the crops rested on the grounds.

Scabbed over rodent feeding on pumpkin. Photo: Marissa Schuh, UMN Extension.

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